1. Field of the Invention
Generally, the present invention relates to the fields of molecular biology and medicine. More specifically, the present invention is in the field of cancer research, especially ovarian cancer diagnosis.
2. Background of the Invention
In order for malignant cells to grow, spread or metastasize, they must have the capacity to invade local host tissue, dissociate or shed from the primary tumor, enter and survive in the bloodstream, implant by invasion into the surface of the target organ and establish an environment conducive for new colony growth (including the induction of angiogenic and growth factors). During this progression, natural tissue barriers such as basement membranes and connective tissue have to be degraded. These barriers include collagen, laminin, fibronectin, proteoglycans and extracellular matrix glycoproteins. Degradation of these natural barriers, both those surrounding the primary tumor and at the sites of metastatic invasion, is believed to be brought about by the action of a matrix of extracellular proteases.
Proteases have been classified into four families: serine proteases, metallo-proteases, aspartic proteases and cysteine proteases. Many proteases have been shown to be involved in human disease processes and these enzymes are targets for the development of inhibitors as new therapeutic agents. Certain individual proteases are induced and overexpressed in a diverse group of cancers, and as such, are potential candidates for markers of early diagnosis and targets for possible therapeutic intervention. A group of examples are shown in Table 1.
TABLE 1Known proteases expressed in various cancersGastricBrainBreastOvarianSerineuPAuPANES-1NES-1Proteases:PAI-1PAI-1uPAuPAtPAPAI-2CysteineCathepsin BCathepsin LCathepsin BCathepsin BProteases:Cathepsin LCathepsin LCathepsin LMetallo-Matrilysin*MatrilysinStromelysin-3MMP-2proteases:Collagenase*StromelysinMMP-8Stromelysin-1*Gelatinase BMMP-9Gelatinase AuPA, Urokinase-type plasminogen activator;tPA, Tissue-type plasminogen activator;PAI-I, Plasminogen activator 0 inhibitors;PAI-2, Plasminogen activator inhibitors;NES-1, Normal epithelial cell-specific-1;MMP, Matrix P metallo-protease.*Overexpressed in gastrointestinal ulcers.
There is a good body of evidence supporting the downregulation or inhibition of individual proteases and the reduction in invasive capacity or malignancy. In work by Clark et al., inhibition of in vitro growth of human small cell lung cancer was demonstrated using a general serine protease inhibitor. More recently, Torres-Rosedo et al. (1993) demonstrated an inhibition of hepatoma tumor cell growth using specific antisense inhibitors for the serine protease hepsin gene. Metastatic potential of melanoma cells has also been shown to be reduced in a mouse model using a synthetic inhibitor (batimastat) of metallo-proteases. Powell et al. (1993) presented evidence to confirm that the expression of extracellular proteases in a non-metastatic prostate cancer cell line enhances their malignant progression. Specifically, enhanced metastasis was demonstrated after introducing and expressing the PUMP-1 metallo-protease gene. There is also a body of data to support the notion that expression of cell surface proteases on relatively non-metastatic cell types increases the invasive potential of such cells.
To date, ovarian cancer remains the number one killer of women with gynecologic malignant hyperplasia. Approximately 75% of women diagnosed with such cancers are already at an advanced stage (III and IV) of the disease at their initial diagnosis. During the past 20 years, neither diagnosis nor five-year survival rates have greatly improved for these patients. This is substantially due to the high percentage of high-stage initial detection of the disease. Therefore, the challenge remains to develop new markers that improve early diagnosis and thereby reduce the percentage of high-stage initial diagnoses. The ability to disengage from one tissue and re-engage the surface of another tissue is what provides for the morbidity and mortality associated with this disease. Therefore, extracellular proteases may be good candidates for markers of malignant ovarian hyperplasia.
Thus, the prior art is deficient in a tumor marker useful as an indicator of early disease, particularly for ovarian cancers. The present invention fulfills this long-standing need and desire in the art.